This invention generally relates to electrodeposition solutions and processes for forming metal containing films, and more particularly, to electrodeposition solutions and processes for depositing films of gallium, indium, a combination thereof, and a combination of any of the preceding with copper.
Current processes for electroplating metal containing thin films such as gallium and gallium alloys present numerous problems. These problems include, among others, low cathodic deposition efficiency due to excessive hydrogen generation, poor repeatability of the process, partly due to the poor cathodic efficiency, and the poor quality of the deposited films such as their high surface roughness and poor morphology. Gallium is generally considered a difficult metal to deposit without excessive hydrogen generation on the cathode because gallium plating potential is relatively high. Hydrogen generation on the cathode causes the deposition efficiency to be less than 100% because some of the deposition current gets used on forming the hydrogen gas rather than for forming the gallium film on the substrate or cathode. Moreover, hydrogen generation and evolution is a causal factor for introducing porosity into the deposited film, thereby contributing to increased surface roughness and microdefects. The plating efficiencies inherently reduce the repeatability of an electrodeposition process because hydrogen generation itself is a strong function of many factors including impurities in the electrolyte, deposition current density, small changes on the morphology or chemistry of the substrate surface, temperature, mass transfer, and the like.
Accordingly, there is a need in the art for improved electroplating processes and chemistries that deposit uniform, substantially defect free, and smooth thin films with high plating efficiency and repeatability.